Phenoxy acid herbicides are members of a family of chemicals related to the growth hormone indoleacetic acid (IAA). When sprayed on a field of crops such as wheat, rice or corn (monocots), phenoxy acid herbicides selectively induce rapid, uncontrolled growth in broad-leaf weeds (dicots) that eventually kills the unwanted vegetation and leaves the crops relatively unaffected. Phenoxy acid herbicides were independently developed in the USA and UK during World War 11 and were first introduced commercially in 1946. Today, 60 years later, the phenoxy acid herbicides still remain among the most widely used herbicides in the world.
There is a wide variety of phenoxy acid herbicides in use, further grouped into the phenoxyacetic, phenoxybutyric, and phenoxypropionic subtypes, the last itself containing the aryloxyphenoxypropionic subtype, which has the greatest number of commercial variants. 2,4-D (2,4-dichlorophenoxyacetic acid) is one well-known example, and the present invention will be exemplified using this herbicide, though the other phenoxy acids can equally well be used in the same types of formulations for the same purposes.
2,4-D acid is a white, crystalline solid, minimally soluble in water, generally formulated as soluble concentrates or emulsifiable concentrates in order to facilitate its application. The soluble concentrates are usually non-volatile, water-soluble formulations of 2,4-D amine salts such as ammonium salt, dimethylamine, isopropylamine, triethylamine, or diethanolamine salts. The emulsifiable concentrates are formulations of, for example, 2,4-D esters with high volatility, such as ethyl, propyl, isopropyl, butyl, isobutyl, or amyl esters, or 2,4-D esters with low volatility, such as butoxyethyl or 2-ethylhexyl esters.
The terms “ammonium” and “monoammonium” are used herein to refer to inorganic ammonium salts, i.e., NH4+, unless the context demands otherwise. Phenoxy acid rates and concentrations given herein, even where the phenoxy acid is present as a salt or salts, are expressed as acid equivalent (ae)—by acid equivalent is meant that portion of a formulation that, theoretically, could be converted back to the parent acid and represents the original acid portion of the molecule—unless the context demands otherwise.
It has been generally accepted that, with the same 2,4-D acid equivalent, the 2,4-D esters are more effective than the 2,4-D amine salts, although their herbicidal effect is slower. The highly volatile esters are also more effective than esters with low volatility, but can cause undesired damage to the surrounding environment because of their volatility. The risk of unwanted damage caused by volatilisation has caused the application of highly volatile ester formulations to be regulated and restricted.
A commonly practised way to enhance the performance of pesticide products is to add an adjuvant either to the pesticide formulation or to the spray tank just before application. An adjuvant can maximise the activity of the pesticide product by a variety of functions, such as increasing spray droplet retention on difficult to wet leaf surfaces, or facilitate penetration of the pesticide into the plant cuticle.
Substances traditionally utilised as adjuvants are, for example, petroleum or natural based oils, inorganic salts, polymers, polyols, and surfactants. Surfactants have proved to be very useful and versatile adjuvants for many applications, but selecting the optimum surfactant system and the optimum concentration for a specific pesticide application is often a challenge.
A type of surfactant that has proved to be especially useful as a pesticide adjuvant in several applications is the amine derivative. An amine surfactant with a primary, secondary or tertiary amine function can react with an acid to form a salt. By using an amine surfactant to neutralise all, or a part of, the 2,4-D acid, it is possible to create a highly concentrated, water-soluble 2,4-D formulation with a built-in adjuvant system.
U.S. Pat. No. 3,276,856 discloses compositions containing dimethyl-(C12-C18 alkyl)amine salts of phenoxy acid herbicides, e.g. 2,4-dichlorophenoxyacetic acid. These compositions have a high level of active herbicidal ingredient and improved emulsification properties, and are used to make water-in-oil emulsions.
US 2005/0215434 teaches to use herbicidal 2,4-D-amine salts, e.g. dimethylamine or diethanolamine salts, in combination with a humectant, such as ethoxylated fatty amines or amine oxides, an anti-freeze, and an anti-foaming agent in order to make liquid compositions that are non-volatile, soluble in water, and stable at low temperatures.
WO 02/32227 describes how to make a non-aqueous homogeneous liquid herbicide composition comprising a lipophilic carrier. Such non-aqueous compositions are not in accordance with the present invention.
WO 01/32019 discloses emulsions comprising a) pesticides and b) fatty acid amidoamines and/or their quaternized derivatives. However, the products disclosed therein are made by, in a first step, reacting fatty acids and unsubstituted ethylene amines. The use of unsubstituted amines will inevitably result in the formation of by-products during the manufacturing, such as hydrophobic diamides, leading to various problems and reduced efficacy. The production of an alkylene oxide-substituted amine B, as disclosed in the examples, by alkoxylation of the unsubstituted amide obtained in the first step, is thus an overall costly multi-step process and will result in the formation of a number of by-products. Hence, alternative, more cost-efficient products are desired. Further, the ethyleneamine-based amides have an inferior biodegradability compared to the propylenediamine-based amides.
In EP 1 289 362 compositions are disclosed containing a) a pesticide and b) an adjuvant which could be an amidoamine. An amidoamine used in the working examples is a cocoamide of N,N-bishydroxyethyl-1,3-propylenediamine, which is used together with the pesticides glyphosate and azoxystrobin respectively. However, the production of this bishydroxyethyl substituted amidoamine is costly, results in the formation of a number of by-products, and the bishydroxyethyl substituted amidoamines have too low efficacy. Hence, more cost-efficient products are desired.
In an article by L. L. Jansen in Weeds (1965), 13(2), 123-130, various amine salts of 2,4-dichlorophenoxyacetic acid are disclosed and their herbicidal activity investigated by greenhouse evaluation. Fatty amines, such as coco, soya, oleyl, and tallow alkylamine, were used as such or as ethoxylated or propoxylated derivatives. Further amine derivatives used were di(long chain alkyl) amines, such as di-coco and di-(H-tallow alkyl)amine, tertiary amines such as methyl-di-(coco alkyl)amine and dimethyl-(coco alkyl)amine, and N-alkyl-1,3-propane-diamines, such as N-oleyl-1,3-propanediamine and N—(C1-9 alkyl)-N,N′-diethyl-1,3-propanediamine. The salts were used in water and/or oil.
As disclosed by Jansen, alkylamine based adjuvants have been used in the past and have proven to have bioefficacy-enhancing ability to 2,4-D. The choice of surfactant can be important, since there are wide variations among surfactants in terms of their ability to enhance the herbicidal efficacy of phenoxy acids for particular applications. Dimethyl cocoalkyl amine of the formula
where R=coco alkyl, was considered to be most closely related to the structure of the adjuvants of the present invention, and was thus chosen as one of the references in the Examples of the present invention.
However, there is still a need for finding a suitable adjuvant with good environmental properties in addition to a good efficacy enhancing property, and it is desirable to develop a stable aqueous phenoxy acid salt formulation which (i) has high phenoxy acid ae loading, (ii) is stable and provides better efficacy than that of commercial phenoxy acid salt formulations, and (iii) has an overall better biodegradability.
These and other objectives are met by the adjuvants and herbicidal formulations of the present invention.